1. Field of the Invention.
The present invention relates to the field of data communication interfaces.
2. Prior Art.
Data devices in a typical data processing system generally communicate with other devices in the system through the use of one or more standard data device interconnection schemes or protocols. By way of specific example, many devices in typical minicomputer and microcomputer systems, such as terminals, printers and the like, are interconnected and/or connected to the CPU using a standard RS-232 line. An RS-232 port is an EIA standard serial data port, with a serial data line plus additional control and/or status lines.
In addition to RS-232 lines, other types of communication lines are also frequently used, including parallel lines and coaxial cable (coax) lines, the latter being of particular interest to the present invention. As the name implies, a coax line is truly a single data line (with return) without provision for any additional status or control lines. Such lines have certain advantages in that they are relatively low cost and easily installed. However, their use is limited to those situations where the communications protocol allows or is compatible with the single line nature of a coax cable. Such lines are frequently found in installations having a number of remote terminals connected to a central main frame computer, such as an IBM computer. In certain situations however, it would be desirable to be able to provide a standard RS-232 plug and interface at each end of a line, but use a coax cable rather than the multiline cable of the RS-232 standard, so that the coax in existing installations could be used for RS-232 communication, and/or coax cable could be run in new installations if desired to reduce the cost of cable installation.